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Date: Wed, 22 Mar 2023 22:08:54 +0000
From: "Zhang, Qiang1" <qiang1.zhang@...el.com>
To: "paulmck@...nel.org" <paulmck@...nel.org>
CC: "frederic@...nel.org" <frederic@...nel.org>,
"joel@...lfernandes.org" <joel@...lfernandes.org>,
"rcu@...r.kernel.org" <rcu@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"qiang.zhang1211@...il.com" <qiang.zhang1211@...il.com>
Subject: RE: [PATCH] srcu: Fix flush sup work warning in cleanup_srcu_struct()
> > > insmod rcutorture.ko
> > > rmmod rcutorture.ko
> > >
> > > [ 209.437327] WARNING: CPU: 0 PID: 508 at kernel/workqueue.c:3167
> > > __flush_work+0x50a/0x540 [ 209.437346] Modules linked in:
> > > rcutorture(-) torture [last unloaded: rcutorture] [ 209.437382]
> > > CPU: 0 PID: 508 Comm: rmmod Tainted: G W 6.3.0-rc1-yocto-standard+
> > > [ 209.437406] RIP: 0010:__flush_work+0x50a/0x540 .....
> > > [ 209.437758] flush_delayed_work+0x36/0x90 [ 209.437776]
> > > cleanup_srcu_struct+0x68/0x2e0 [ 209.437817]
> > > srcu_module_notify+0x71/0x140 [ 209.437854]
> > > blocking_notifier_call_chain+0x9d/0xd0
> > > [ 209.437880] __x64_sys_delete_module+0x223/0x2e0
> > > [ 209.438046] do_syscall_64+0x43/0x90 [ 209.438062]
> > > entry_SYSCALL_64_after_hwframe+0x72/0xdc
> > >
> > > For srcu objects defined with DEFINE_SRCU() or DEFINE_STATIC_SRCU(),
> > > when compiling and loading as modules, the srcu_module_coming() is
> > > invoked, allocate memory for srcu structure's->sda and initialize
> > > sda structure, due to not fully initialize srcu structure's->sup, so
> > > at this time the sup structure's->delaywork.func is null, if not
> > > invoke init_srcu_struct_fields() before unloading modules, in
> > > srcu_module_going() the __flush_work() find
> > > work->func is empty, will raise the warning above.
> > >
> > > This commit add init_srcu_struct_fields() to initialize srcu
> > > structure's->sup, in srcu_module_coming().
> > >
> > > Signed-off-by: Zqiang <qiang1.zhang@...el.com>
> > >
> > >Good catch, and thank you for testing the in-module case!
> > >
> > >One question below...
> > >
> > > Thanx, Paul
> > >
> > > ---
> > > kernel/rcu/srcutree.c | 11 ++++++++---
> > > 1 file changed, 8 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index
> > > 1fb078abbdc9..42d8720e016c 100644
> > > --- a/kernel/rcu/srcutree.c
> > > +++ b/kernel/rcu/srcutree.c
> > > @@ -1921,7 +1921,8 @@ static int srcu_module_coming(struct module *mod)
> > > ssp->sda = alloc_percpu(struct srcu_data);
> > > if (WARN_ON_ONCE(!ssp->sda))
> > > return -ENOMEM;
> > > - init_srcu_struct_data(ssp);
> > > + if (WARN_ON_ONCE(init_srcu_struct_fields(ssp, true)))
> > > + return -ENOMEM;
> > >
> > >Wouldn't it be better to simply delete the init_srcu_struct_data()?
> > >
> > >Then the first call to check_init_srcu_struct() would take care of
> > >the initialization, just as for the non-module case. Or am I missing
> > >something subtle?
> >
> > Hi Paul
> >
> > Maybe the check_init_srcu_struct() is always not invoked, for example,
> > In rcutorture.c, here is such a definition DEFINE_STATIC_SRCU(srcu_ctl),
> > but we use torture_type=rcu to test, there will not be any interface
> > calling
> > check_init_srcu_struct() to initialize srcu_ctl and set
> > structure's->delaywork.func is process_srcu().
> > when we unload the rcutorture module, invoke cleanup_srcu_struct() to
> > flush sup structure's->delaywork.func, due to the func pointer is not
> > initialize, it's null, will trigger warning.
> >
> > About kernel/workqueue.c:3167
> >
> > __flush_work
> > if (WARN_ON(!work->func)) <---------trigger waning
> > return false;
> >
> >
> > and in init_srcu_struct_fields(ssp, true), wil set
> > srcu_sup->sda_is_static is true and set srcu_sup-> srcu_gp_seq_needed
> > is zero, after that when we call
> > check_init_srcu_struct() again, it not be initialized again.
> >
> >
> >Good point! In the non-module statically allocated case there is never a call to cleanup_srcu_struct().
> >
> >So suppose the code in srcu_module_coming() only did the alloc_percpu(), and then the
> >code in srcu_module_going() only did the the matching
> >free_percpu() instead of the current cleanup_srcu_struct()?
>
> But in modules, for srcu objects defined with DEFINE_SRCU() or DEFINE_STATIC_SRCU(),
> when a module is unloaded, we usually don't call cleanup_srcu_struct() in the module
> unload function.
> If in srcu_module_going() only do free_percpu(), the srcu_sup->node memory maybe
> can not free and also lost the opportunity to refresh the running work.
>
>
>But in the module case, isn't the srcu_sup->node also statically
>allocated via the "static struct srcu_usage" declaration?
static bool init_srcu_struct_nodes(struct srcu_struct *ssp, gfp_t gfp_flags)
{
sp->srcu_sup->node = kcalloc(rcu_num_nodes, sizeof(*ssp->srcu_sup->node), gfp_flags);
...
}
Regardless of whether the srcu object is declared in the module or not, sup->node is dynamically allocated.
right?
Thanks
Zqiang
>
> Thanx, Paul
>
>------------------------------------------------------------------------
>
>#ifdef MODULE
># define __DEFINE_SRCU(name, is_static) \
> static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \
> is_static struct srcu_struct name = __SRCU_STRUCT_INIT_MODULE(name, name##_srcu_usage); \
> extern struct srcu_struct * const __srcu_struct_##name; \
> struct srcu_struct * const __srcu_struct_##name \
> __section("___srcu_struct_ptrs") = &name
>#else
># define __DEFINE_SRCU(name, is_static) \
> static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data); \
> static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \
> is_static struct srcu_struct name = \
> __SRCU_STRUCT_INIT(name, name##_srcu_usage, name##_srcu_data)
>#endif
>
> Thanks
> Zqiang
>
>
> >
> > Thanx, Paul
> >
> > Thanks
> > Zqiang
> >
> > >
> > >It should also be possible to eliminate duplicate code between the
> > >in-module and non-module statically allocated initialization cases,
> > >come to think of it.
> > >
> > > }
> > > return 0;
> > > }
> > > @@ -1931,9 +1932,13 @@ static void srcu_module_going(struct module
> > > *mod) {
> > > int i;
> > > struct srcu_struct **sspp = mod->srcu_struct_ptrs;
> > > + struct srcu_struct *ssp;
> > >
> > > - for (i = 0; i < mod->num_srcu_structs; i++)
> > > - cleanup_srcu_struct(*(sspp++));
> > > + for (i = 0; i < mod->num_srcu_structs; i++) {
> > > + ssp = *(sspp++);
> > > + cleanup_srcu_struct(ssp);
> > > + free_percpu(ssp->sda);
> > > + }
> > >
> > >And good catch on another memory leak with this one, looks proper to
> > >me.
> > >
> > > }
> > >
> > > /* Handle one module, either coming or going. */
> > > --
> > > 2.25.1
> > >
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